The isostatic bulge forming process for forming blank parts employs a pressure vessel that can be pressurized up to about 20,000 lbs/in2 (PSI) or greater. For the forming operation a blank part, such as a tube blank, is placed into two mating female die sections that are bolted together to contain the blank part where an area between the outer surface of the blank part and an interior working surface of the die cavity is sealed off with a suitable seal that prevent pressurized forming fluid from entering the die cavity. The ends of the blank part are open to a forming fluid contained in the pressure vessel so that as the pressure of the forming fluid increases the forming fluid exerts pressure on an inner surface of the blank part thereby expanding or otherwise pressing the outer surface of the blank part against the working surface of the die cavity.
As a result of the seal preventing forming fluid entry into the die cavity air that is trapped within the die cavity cannot escape and is compressed during forming of the blank part. This compressed air may be sufficient to prevent full formation of the blank part and in some instances causes a reverse form (e.g. denting in) of the tube blank which results in a deformed part. Conventionally, the air in the die cavity is released in a two part forming process where the tube blank is partially formed, the die is removed from the pressure vessel and the die sections are unbolted or separated to release the compressed/pressurized air in the die cavity. The die sections are reassembled and the die is placed back into the pressure vessel where the forming process is repeated to completely form the blank part. Removal of the die from the pressure vessel, disassembling the die to release the air in the die cavity, reassembling the die and repeating the forming process is laborious and time consuming which increases the production cost of forming the blank part.